[Show abstract][Hide abstract]ABSTRACT:
The aim of the present study was to assess the incremental benefit of compensating asynchronous cardiac quiescence in coronary wall MR imaging. With the approval of IRB, black-blood coronary wall MR imaging was performed on 30 older subjects (90 coronary wall segments). For round 1 coronary wall MR imaging, acquisition windows were traditionally set within rest period4-chamber. Totally 51 of 90 images were ranked as "good" images and resulted in an interpretability rate of 57 %. Then, an additional cine-MR was centered at coronary segments to obtain rest periodcross-sectional. The rest periodoverlap (the intersection between rest period4-chamber and rest periodcross-sectional) was measured for each coronary segment. The "good" images had a longer rest periodoverlap and higher acquisition coincidence rate (the percentage of acquisition window covered by the rest periodoverlap) than "poor" images. Coronary wall rescans (round 2) were completed at 39 coronary segments that were judged as having "poor" images in round 1 scans. The acquisition window was set within the rest periodoverlap. For the round 2 images, 17 of 39 (44 %) coronary segments were ranked as "good" images. The overall interpretability rate (68 of 90, 76 %) was significantly higher than that of the round 1 images alone. Our data demonstrated that asynchronous cardiac quiescence adversely affects the performance of coronary wall MR imaging. Individualizing acquisition windows based on multi-plane cine-MR helps to compensate for this motion discrepancy and to improve image quality.

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grade of 1, 2, or 3 was considered eligible for quanti-tative analysis/comparison.Black-bloodimages ofzoomed to 1000%. The eligible coronary borders (withimage grades 1, 2, 3) were manually traced by oneexperienced radiologist (with 5 years experience ofcardiovascular imaging) using VesselMASS software(Leiden University, the Netherlands). The area of thevessel wall was defined as the area between the outerwall and the lumen. The mean thickness of the vesselwall and lumen area was calculated automaticallyaccording to vessel contours. The signal-to-noise ratio(SNR, SI wall / SD noise) and the contrast-to-noise ra-tio (CNR [SI wall?SI lumen]/SD noise) of the coronaryartery wall vs. lumen were also calculated (11–13).The noise was measured in the pictures where therewere no anatomic structures or artifacts.thecoronarywallwereStatistical MethodsData are presented as mean 6 one standard deviation(SD). General image quality was compared betweenSSFP and TSE using the Mann–Whitney U-test. TheSNR and CNR of the two imaging techniques (SSFP vs.TSE) were compared with the t-test. Pearson correla-tion efficient and Bland–Altman plots were applied toevaluate agreements of vessel wall area and wall thick-ness measured on matched SSFP and TSE images. Allstatistical analysis was performed with SPSS software(v. 13.0, Chicago, IL). For all calculations and results,P < 0.05 was considered statistically significant.RESULTSGeneral Image QualityTwo patients were excluded because they had metalresidues (pacing wires) in the body. In total, 28 scanswere completed. The length of cardiac rest periodswas 53 6 27 msec. In total, 19 coronary segments(with TSE) and 40 coronary segments (with SSFP)were carried out for quantitative analysis (grades 1, 2,3). Seventeen pairs of coronary images (from 15patients) were matched for the same anatomy.Coronary Indices ComparisonThe image quality score for SSFP was higher than forTSE (1.23 6 0.95 vs. 0.88 6 0.69, P < 0.001). Com-pared with TSE, SSFP had a higher mean coronarywall SNR (20.1 6 8.5 vs. 14.9 6 4.8, P < 0.001) andwall-lumen CNR (8.2 6 4.6 vs. 6.8 6 3.7, P ¼ 0.005)(see Figs. 1–3 for images of three typical cases; see Ta-ble 2 for data summary). Good agreements of wallarea and thickness measurements between SSFP andTSE were observed on matched coronary images, withPearson correlation coefficients of 0.783 and 0.624,respectively (P < 0.001) (Figs. 4, 5).DISCUSSIONIn this study we report the feasibility of imaging coro-nary wall in cardiac allografts using black-blood SSFPMRI. Compared with traditional TSE, SSFP offers bet-ter image quality, higher SNR and CNR, with compa-rable coronary measurements under conditions of fastheart rate in HTx patients.According to data from the registry of the Interna-tional Society of Heart and Lung Transplantation(ISHLT), ?3300 heart transplants were performed inNorth America in 2008 as a final solution to irreversi-ble heart failure (13). However, many serious compli-cations follow this high-cost treatment. Due to con-tinuing humoral and cell-mediated responses by therecipient to human leukocyte antigen (HLA) present inFigure 1. A 55-year-old male who had a heart transplant 2 years ago. Heart rate: 76 bpm. The LM could be clearly seen onboth SSFP (Grade 3) and TSE (Grade 3) images. a: SSFP. b: TSE.1212 Lin et al.

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the donor tissue, CAV, also known as chronic rejec-tion, is a leading cause of graft loss and death inpatients who survive the first year after transplanta-tion (1). In some cases, undetected CAV may silentlycause graft failure with global ischemia without docu-mented signs of infarction or pathology on ECG (1).Sometimes, CAV may develop quickly and serial fol-low-up imaging of cardiac allografts is absolutelyessential. Therefore, MR coronary wall imaging, fea-tured as ‘‘noninvasive’’ and ‘‘no radiation,’’ is expectedto be an ideal candidate for examining HTx recipients.However, cardiac motion has always been consideredto be a major technical impediment to clinical use ofcoronary wall MRI. Rapid heart rate, which is posi-tively related to severe cardiac motion, has become amain barrier restricting HTx patients from suchexaminations (14,15).In various research studies, TSE has already beenaccepted as the conventional technique for black-blood coronary wall imaging (16–18). It requires shortecho trains to limit signal decay (T2 decay) caused bytransverse relaxation and to minimize cardiac motionduring signal readout (19,20), resulting in a relativelylong imaging time. For TSE coronary wall MRI, theFigure 2. A 73-year-old female who had a heart transplant 5 years ago. Heart rate: 96 bpm. The LAD could be depicted onboth SSFP (Grade 3) and TSE (Grade 1). Visually, the image quality of SSFP is better. a: SSFP. b: TSE.Figure 3. A 61-year-old female who had a heart transplant 7 years ago. Heart rate: 108 bpm. The RCA can only been seenon SSFP (Grade 3), but not on TSE. a: SSFP. b: TSE.Coronary MRI for Cardiac Allografts1213

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reduced number of k-space lines (lower acquisitiontime during signal cardiac cycle) acquired per cardiaccycle may be a possible solution for the short rest pe-riod caused by a high heart rate. However, a directconsequence of this strategy is the longer gross imag-ing time, which may result in more unexpectedmotion artifacts and irregular breathing modes. All ofthem may significantly reduce image quality. Betablockers have been routinely used to improve imagequality in coronary CT angiography by reducing heartrates. However, the long-term effects of beta blockerson HTx patients have not been thoroughly studied.Therefore, we did not apply them in our study.Balanced SSFP sequences have a shorter imagingtime than TSE for vessel wall imaging. As in high heartrate conditions, the ‘‘rest period’’ of cardiac motion isusually short (10). When balanced SSFP is applied tocoronary wall MRI, a shorter data acquisition windowavailable in cardiac cycles much more easily fulfills theneeds of SSFP than that of TSE. Hence, time efficiencybecomes a valuable characteristic of SSFP for coronarywall imaging in HTx patients.Furthermore, with a gradient structure that is bal-anced in all directions (readout, phase-encoding, andpartition-encoding), balanced SSFP allows for a highflip angle without substantial signal decay. SSFPacquires images at a faster speed, using a higherreadout bandwidth and shorter TR as compared toTSE. Hence, both a balanced gradient structure and ashorter acquisition time may together contribute toless signal loss and intravoxel dephasing caused bycardiac motion (21).Our study had several limitations. First, the samplesize of eligible coronary segments was relatively smallfor quantitative comparison. Under conditions of fastheart rate, the success rate of coronary MRI is reallylow, especially for TSE. However, it is well known thatelevated heart rate is a main adverse factor for coro-nary imaging. In this feasibility study we demonstratedthe advantage of SSFP in coronary imaging and makesome progress in solving this problem. Second, wewere unable to identify any specific lesions of the ves-sel wall, such as CAV. This might be due to our stableand asymptomatic HTx patients and limited coverageof 2D coronary wall MRI. However, our results affirmthe capability of SSFP coronary wall MRI for acquiringimportant indices for monitoring CAV, such as coro-nary wall area and wall thickness. As proven byanother study, the spatial resolution should be appro-priate to find coronary wall thickening (3).In conclusion, 2D DIR-prepared SSFP coronary wallMRI has higher image quality as compared with 2DDIR TSE in HTx patients. It has the potential to serveas an eligible option of coronary wall MRI for cardiacallografts under fast heart rate conditions.REFERENCES1. Schmauss D, Weis M. Cardiac allograft vasculopathy: recentdevelopments. Circulation 2008;117:2131–2141.2. Bastarrika G, Broncano J, Arraiza M, et al. Systolic prospectivelyECG-triggered dual-source CT angiography for evaluation of thecoronary arteries in heart transplant recipients. Eur Radiol 2011;21:1887–1894.3. Miao C, Chen S, Macedo R, et al. Positive remodeling of the coro-nary arteries detected by magnetic resonance imaging in anasymptomatic population: MESA (Multi-Ethnic Study of Athero-sclerosis). J Am Coll Cardiol 2009;53:1708–1715.4. Hofman MB, Wickline SA, Lorenz CH. Quantification of in-planemotion ofthecoronaryarteries duringthe cardiaccycle:Table 2Image Quality and ComparisonsSSFP TSEPImage scores(mean rank)SNRCNRWall thickness (mm)Lumen area (mm2)1.2360.95 0.8860.69<0.00120.168.58.264.61.3760.358.8362.7614.964.86.863.71.3160.289.1163.11<0.001¼0.005¼0.898¼0.324Imaging scores were compared on 84 coronary positions from 28participants. SNR and CNR were compared on SSFP (40 coronarysegments) and TSE (19 coronary segments). Wall thickness andlumen area were compared on SSFP (17 segments) and TSE (17matched segments).Figure 4. Bland–Altman plot of measurements of coronarywall thickness with SSFP and TSE. r ¼ 0.783.Figure 5. Bland–Altman plot of measurements of coronarylumen area with SSFP and TSE. r ¼ 0.624.1214 Lin et al.